Abstract: Biostratigraphic Correlation of Mesaverde Group in Southwestern Wyoming and Northwestern Colorado

F. X. Miller

The Mesaverde Group in southwestern Wyoming and northwestern Colorado represents a complex intertonguing of the Upper Cretaceous (Montanan) marine strata of eastern Wyoming and Colorado with the nonmarine strata of north-central Utah. Paleontologic control in the marine strata is sufficient to permit accurate biostratigraphic correlations based on time. In the west, paleontologic data from the nearshore marine and continental deposits are incomplete or absent. As a result, current stratigraphic correlations of the Mesaverde Group are based on nonsynchronous lithologic data.

The stratigraphic correlations presented are based on palynologic microfossils identified in samples from wells and outcrop sections in Wyoming and Colorado. Time lines to illustrate the chronostratigraphic relation of the Mesaverde Group in different basins are established using the stratigraphic ranges of the palynologic microfossils and the graphic correlation technique of Shaw. Formation names within the Mesaverde Group differ from basin to basin. This paper places the various formations comprising the Mesaverde Group in the Rock Springs uplift and the Green River, Washakie, Sand Wash, and northern Piceance basins in their proper chronostratigraphic order.

Evidence of a widespread unconformity within the Mesaverde Group is present. Broad regional arching accompanied by erosion occurred over most of southwestern Wyoming prior to deposition of the Ericson Sandstone. The extent of the unconformity and its overall effect on the stratigraphic section have not been fully realized in the past. Recognition of this unconformity requires a reinterpretation of the depositional and tectonic history of the Mesaverde Group of southwestern Wyoming. This interpretation coincides with known events in the Powder River, Big Horn, and Great Divide basins.

AAPG Search and Discovery Article #90969©1977 AAPG-SEPM Rocky Mountain Sections Meeting, Denver, Colorado